White india ink

Abstract

To provide a white India ink that achieves superior opacity.SOLUTION: A white India ink comprising titanium oxide particles as a pigment and aluminum particles as an opacifier, the content of the titanium oxide particles being 30 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to white ink. [Background technology]

[0002] Previously, studies have been conducted on the color development properties of ink. For example, Patent Document 1 describes an ink composition containing titanium oxide particles as a hiding agent, along with an aluminum pigment for imparting a glittering effect. With this ink composition, the aluminum pigment is applied to a coating surface such as a paper surface while the coating surface is blocked and hidden by the titanium oxide particles, and it is believed that this ink composition produces drawn lines with a high brightness and metallic luster. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-147676 Summary of the Invention [Problem to be solved by the invention]

[0004] White India ink is sometimes used as ink. For example, white characters written on a highly saturated red or low-brightness black paper surface can give a unique impression to the viewer. To prevent the color of the paper surface from showing through in the coating, such as in the writing lines, it is possible to use titanium oxide particles, which are known as a pigment with high hiding power.

[0005] However, the present inventors have found that when they apply white ink containing titanium oxide particles to the above-mentioned paper surface, the color of the paper surface shows through in the coating film, even when a relatively large amount of titanium oxide particles is included. This is thought to be because titanium oxide particles, which have hiding power, are unable to exhibit sufficient hiding power on the above-mentioned paper surface.

[0006] In view of the above circumstances, an object of the present invention is to provide a white ink having excellent hiding power. [Means for solving the problem]

[0007] The white ink according to the present invention is The ink contains titanium oxide particles as a pigment and aluminum particles as a hiding agent, The content of the titanium oxide particles is 30% by mass or more.

[0008] One embodiment of the white ink according to the present invention is: The mass ratio of the aluminum particles to the titanium oxide particles is 0.05 or less.

[0009] One embodiment of the white ink according to the present invention is: The content of the aluminum particles is 1% by mass or less.

[0010] One embodiment of the white ink according to the present invention is: The aluminum particles are rounded and scale-like.

[0011] One embodiment of the white ink according to the present invention is: The aluminum particles are silica-coated aluminum particles. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a white ink having excellent hiding power. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, white ink as an embodiment of the present invention will be described.

[0014] The white ink of this embodiment contains titanium oxide particles as a pigment, aluminum particles as a hiding agent, and water as a solvent. The white ink is usually used with an applicator equipped with a tip having a fiber bundle. The applicator may be a brush without a storage section for the white ink, or a brush pen equipped with such a storage section. The white ink is used to form a white coating surface on colored paper such as Japanese paper, Xuan paper, or calligraphy paper. Examples of the paper include paper colored to include an R (particularly 1R to 9R) on the Munsell color wheel, such as red (R) or yellow-red (YR), and paper colored to have a Munsell value of 5 or less.

[0015] The titanium oxide particles are usually surface-treated to inactivate the catalytic activity. The surface treatment may be a coating with at least one of inorganic oxide hydrates such as alumina, silica, and zirconia, or a treatment with a fatty acid such as stearic acid. Among these, a coating with an inorganic oxide hydrate is preferred because it can enhance the hydrophilicity of the titanium oxide particles. Furthermore, a silica coating is more preferred because it can enhance the hiding power in addition to the hydrophilicity.

[0016] The titanium oxide particles may be dispersed in the water by a resin emulsion. The resin emulsion prevents the titanium oxide particles (or the aluminum particles) from penetrating into the paper, allowing the formation of a coating surface with a high particle density. Examples of resins that form such resin emulsions include acrylic resins, styrene-acrylic resins, polystyrene resins, vinyl chloride resins, vinyl acetate resins, and vinyl chloride-vinyl acetate copolymer resins. Among these, vinyl acetate resins are preferred.

[0017] The titanium oxide particles preferably have a rutile crystal structure.

[0018] The content of the titanium oxide particles is 30% by mass or more, preferably 35% by mass or more, based on the mass of the white ink. The content of the titanium oxide particles is preferably 50% by mass or less. The content of the titanium oxide particles preferably does not exceed twice the mass of the water (i.e., the relationship: content of the titanium oxide particles < (mass of the water) × 2) is preferably satisfied.

[0019] The aluminum particles typically have an outer layer to prevent aluminum from deteriorating. Specifically, the aluminum particles have a flaky core made of aluminum, which is covered with the outer layer. The core is preferably a silver dollar (high brightness) type flaky core with rounded edges in a planar view. The core may contain unavoidable impurities.

[0020] The outer layer is preferably formed of silica. That is, the aluminum particles are preferably silica-coated aluminum particles. By providing a silica layer that can enhance hydrophilicity, the dispersibility of the aluminum particles in water is improved. Alternatively, the outer layer may be formed by treating the surface of the aluminum core with phosphoric acid or molybdic acid. The molybdic acid may be, for example, a molybdate salt such as ammonium molybdate, or polymolybdic acid. These surface treatment agents may be used alone or in combination of two or more.

[0021] The aluminum particles are preferably flaky, and more preferably silver dollar (high brightness) type flaky particles with rounded edges in a plan view. Compared with corn flake type particles with jagged edges, silver dollar type aluminum particles can reduce the size of the gaps between particles when forming a coated surface, which is thought to improve the hiding power of the coated surface.

[0022] The average particle size of the aluminum particles measured using a particle size distribution measuring device by dynamic light scattering is, for example, 5 to 30 μm.

[0023] Regarding the content of the aluminum particles, the mass ratio of the aluminum particles to the titanium oxide particles (mass of the aluminum particles / mass of the titanium oxide particles) is preferably 0.05 or less, more preferably 0.03 or less, and even more preferably 0.02 or less. Furthermore, the mass ratio here is preferably 0.005 or more. Silver dollar type aluminum particles have a lustrous appearance, and may impart a metallic feel to the coated surface. In consideration of this, the upper limit of the mass ratio described above is preferred.

[0024] The content of the aluminum particles may be 0.1% by mass or more and 1% by mass or less, or 0.4% by mass or more and 1% by mass or less, relative to the mass of the white ink.

[0025] The white ink preferably further contains a binder. Examples of the binder include resin emulsions. Examples of the resin emulsion include alkyl acrylate copolymer emulsions, alkyl acrylate-styrene copolymer emulsions, and alkyl acrylate-vinyl acetate copolymer emulsions. These copolymers may form salts, such as ammonium salts. The alkyl acrylate copolymer is a copolymer of two or more monomers selected from the group consisting of alkyl acrylate, alkyl methacrylate, acrylic acid, and methacrylic acid. The alkyl acrylate-styrene copolymer is a copolymer of styrene and two or more monomers selected from the group consisting of alkyl acrylate, alkyl methacrylate, acrylic acid, and methacrylic acid. The alkyl acrylate-vinyl acetate copolymer is a copolymer of vinyl acetate and two or more monomers selected from the group consisting of alkyl acrylate, alkyl methacrylate, acrylic acid, and methacrylic acid.

[0026] The content (solid content) of the vehicle is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 10% by mass or less, and even more preferably 3% by mass or more and 5% by mass or less, relative to the mass of the white ink.

[0027] The white ink preferably further contains a drying accelerator. The drying accelerator is preferably a solvent that is liquid at room temperature (25°C) and has a boiling point lower than that of water, more preferably a solvent with a boiling point of 85°C or lower. Examples of such solvents include alcohol-based solvents such as methanol, ethanol, and isopropanol, and ketone-based solvents such as acetone and methyl ethyl ketone. The inclusion of the drying accelerator allows the white ink to be quickly fixed to the paper surface. This is particularly preferable for a coating film that is thinly spread with the vehicle on thin paper such as Japanese paper or calligraphy paper, as it allows the coating surface to be formed before the titanium oxide particles excessively penetrate the paper surface.

[0028] The mass ratio of the drying accelerator to the mass of the water is preferably 0.04 or more, and more preferably 0.05 or more. Furthermore, this mass ratio may be 1 or less, or may be 0.5 or less. The content of the drying accelerator relative to the mass of the white ink is preferably 0.5% to 5% by mass, and more preferably 1% to 2.5% by mass.

[0029] The water is preferably purified water such as distilled water or deionized water. The content of the water is preferably 5% by mass or more and 40% by mass or less, and more preferably 20% by mass or more and 30% by mass or less, based on the mass of the white ink.

[0030] The white ink may contain other additives. Examples of the additives include a surfactant, an antifoaming agent, and a preservative. The surfactant is preferably an anionic surfactant or a nonionic surfactant, and more preferably both.

[0031] As described above, the embodiments have been shown as examples, but the white ink according to the present invention is not limited to the configuration of the above-mentioned embodiments. Furthermore, the white ink according to the present invention is not limited by the above-mentioned effects. The white ink according to the present invention can be modified in various ways without departing from the gist of the present invention. [Example]

[0032] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[0033] [Raw materials used] White pigment: Titanium oxide particles (Titanium Paste D, rutile type, containing vinyl acetate resin emulsion, titanium dioxide concentration 60% by mass, manufactured by Miki Riken Kogyo Co., Ltd.) Masking agent: Aluminum particles (Toyo Aluminum Co., Ltd. aluminum paste EMR D4690, aluminum particle concentration 50% by mass) Veneering agent: alkyl acrylate copolymer resin emulsion (Toa Gosei Co., Ltd. alkyl acrylate copolymer, Jurimer AT-510, solids concentration 30% by mass) Drying accelerator: Ethanol (Enekin F-15 manufactured by Japan Alcohol Sales Co., Ltd.) Surfactant: Sodium oleate (NOF Corporation's Nonsal O-NA, an anionic surfactant) Surfactant: Polyoxyalkylene alkyl ether (Noigen LF-60X, a nonionic surfactant manufactured by Daiichi Kogyo Co., Ltd.) Defoaming agent (mixed defoaming agent)

[0034] Using the raw materials shown in Tables 1 to 3, white ink was prepared according to or in accordance with the following production example.

[0035] [Manufacturing example] A surfactant was added to a container containing water while stirring, and the mixture was stirred for 3 minutes. Next, titanium oxide particles and aluminum particles were added while stirring, and the mixture was stirred for 3 minutes. Next, an alkyl acrylate copolymer resin emulsion and ethanol were added, and the mixture was stirred for 3 minutes. Finally, a mixed antifoaming agent was added, and the mixture was stirred for 5 minutes to produce white ink.

[0036] [Evaluation method] Using the prepared white ink and a calligraphy brush, characters were written on red Xuan paper, and after the coating film had dried, the coating film was visually observed and evaluated for hiding power according to the following evaluation criteria. In addition to hiding power, the whiteness and degree of abrasion were also evaluated according to the following evaluation criteria. The results are shown in Tables 1 to 3. (Evaluation criteria for concealment) ○: No red color is observed in most of the strokes. △: Red is observed in some strokes. ×: Red is observed in many strokes. (Evaluation criteria for whiteness) ◯: No gray color originating from aluminum particles is observed, and the white color is strong. ×: Gray color due to aluminum particles is observed, and white coloring is weak. (Rubbing evaluation criteria) ○: Most strokes are hardly rubbed off. ×: The longer the stroke, the more likely it is to rub.

[0037] [Table 1]

[0038] [Table 2]

[0039] [Table 3]

Claims

1. The ink contains titanium oxide particles as a pigment and aluminum particles as a hiding agent, White ink, wherein the content of the titanium oxide particles is 30% by mass or more.

2. 2. The white ink according to claim 1, wherein the mass ratio of the aluminum particles to the titanium oxide particles is 0.05 or less.

3. 3. The white ink according to claim 2, wherein the content of the aluminum particles is 1% by mass or less.

4. The white ink according to claim 1 , wherein the aluminum particles are rounded and scaly.

5. The white ink according to claim 1 , wherein the aluminum particles are silica-coated aluminum particles.

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